Douglas Isbell
Headquarters, Washington, DC March 22, 1995
(Phone: 202/358-1753)
Peter Waller
Ames Research Center, Mountain View, CA
(Phone: 415/604-3938)
RELEASE: 95-34
TESTS SHOW GALILEO PROBE SET FOR FLIGHT TO JUPITER
Key operational tests of the atmospheric probe on
NASA's Jupiter-bound Galileo spacecraft have been
successfully completed, demonstrating that the probe is in
good health and ready for the first-ever descent into the
atmosphere of an outer planet this December.
The just-completed testing followed NASA's first
interrogation of the atmospheric probe in 27 months, and "it
went perfectly," said Marcie Smith, Galileo probe project
manager at NASA's Ames Research Center, Mountain View, CA.
The probe now stands ready to separate from the Galileo
orbiter spacecraft in July and then fly the remaining 50
million miles of its flight to Jupiter on a solo trajectory.
"We wanted to be sure the power system was in good
shape, and it was," Smith said, "and so were the other probe
systems."
"The recent probe tests showed that each of its three
lithium battery modules were operating normally," said
Charles Sobeck, probe engineering manager. Both
accelerometers of the atmosphere structure experiment were
normal. The sampling chamber of the Neutral Mass
Spectrometer, which will analyze the composition of
Jupiter's atmosphere, was pumped out in preparation for
descent.
"Engineers also conducted an end-to-end test of the
probe data compression system, and it worked very well,"
Sobeck said. Command systems for the two redundant data
systems worked without a flaw, as did the data return link
for the primary system.
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Further data on the operation of the probe radio
receiver aboard the orbiter will be returned and analyzed in
coming weeks.
Upon its arrival at Jupiter on December 7, 1995, the
probe willmake the first entry into the atmosphere of one of
the solar system's giant gas planets. This will be the most
difficult planetary entry ever attempted, with the probe
expected to reach a speed of 106,000 mph before it
encounters deceleration forces of up to 350 G's (350 times
Earth gravity) through friction with Jupiter's atmosphere.
After entry, the probe will descend about 400 miles
into the planet's complex atmosphere, making the first
direct measurements of its clouds, lightning, winds and
other features.
Jupiter is the largest planet in the solar system, with
about 300 times the mass of the Earth. The planet has its
own internal heat source, and its spectacular banded
appearance and many other active cloud features such as the
Great Red Spot make its atmosphere a topic of great
scientific interest.
NASA engineers last communicated with the probe in
November and December 1992. At that time, it was in
"excellent shape," Smith said. While the vacuum of space is
considered a safe environment for non-operating spacecraft,
"it will be six years after the batteries were built before
they get used to power the probe," she explained, "so we
wanted to check them one more time before release."
After deploying the probe, the Galileo orbiter will
change its course to pass 133,000 miles above Jupiter's
clouds, while the probe continues on and descends into the
atmosphere. The probe will radio its data to the orbiter,
which will store it for later transmission to Earth before
beginning two years of orbital-based observations of
Jupiter, its moons and its powerful magnetosphere.
"We are delighted that the probe checkout went so
well," said Galileo Project Manager William J. O'Neil of
NASA's Jet Propulsion Laboratory, Pasadena, CA. The
successful probe checkout was the first activity to be
carried out under new Galileo flight software that was
transmitted to the spacecraft in January and February,
indicating that all of the major elements of the mission are
ready for the start of its encounter with Jupiter.
The Galileo probe project is managed by NASA Ames. The
overall Galileo mission is managed by NASA's Jet Propulsion
Laboratory. The probe was built by Hughes Aircraft Co., El
Segundo, CA.
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